Inflammatory agents such as the prostaglandins (PGs) are known to sensitize sensory neurons to subsequent stimulation, resulting in a condition of heightened sensitivity known as hyperalgesia. At present we that inflammatory PGS enhance the sensitivity and excitability of sensory neurons through activation of the cAMP transduction cascade. However, very little is known regarding the regulatory mechanisms and transduction cascades controlling the intensity or duration of the enhanced sensitivity that results in neurogenic aspects of the inflammatory response and hyperalgesia. The proposed studies seek to establish the physiological mechanisms whereby the calcium,/nitric oxide/cGMP pathways lead to inactivation of the enhanced excitability or sensitization of sensory neurons. The hypothesis of this proposal is that cGMP, through activation of cGMP- dependent protein kinase (PKG) and its possible modulation of other intracellular mediators, alters the properties or state of various membrane currents to reverse the enhanced neuronal excitability produced by the cAMP/PKA pathway. The studies outlined in this proposal will use rat dorsal root ganglion cells grown in culture as a model system. The electrophysiological properties of these neurons will be examined with the patch-clamp technique. This allow measurement of membrane currents arising from the whole cell or single-ion channels. In conjunction with patch-clamp recordings, changes in the concentration of intracellular calcium, cAMP, and cGMP will be measured and correlated to the observed alterations in neuronal excitability. The specific aims of this proposal are: 1) To quantify the changes in intracellular calcium concentration using fluorescent calcium indicators and thus determine directly the contributions of calcium to the activation of signaling pathways involved in the inactivation of sensitization; 2) To establish a fundamental understanding of the different transduction cascades and to determine whether the inactivating pathways are specific to the nature of the stimulus or part of a more generalized cellular design; 3) To determine the specific intracellular mediators and their mechanisms of action that give rise to the inactivation of sensitization. This will provide an initial step in determining the specific target proteins that are modulated by the mediator(s) of inactivation. Ultimately, if we can establish the regulatory mechanism modulating the up and down regulation of excitability, it will be possible to design therapies that selectively modulate the altered pathway and thus curb the persistent pain and heightened sensitivity associated with chronic inflammatory conditions, such as rheumatoid arthritis.